Thin film integrated circuits are manufactured in a multi-step process wherein successive layers of conductive, semi-conductive and insulative materials are formed to create an integrated set of transistors. In order to create the appropriate structure for each of the materials in the device, various metallic patterns are deposited onto the substrate followed by selective etching to form the circuit. The term, etching, as used in the art of microelectronic fabrication, relates to a process wherein metallic material is removed from a substrate or from thin films deposited on the substrate's surface.
Traditional etching methods are carried out using "wet" techniques wherein a metallic surface to be etched is immersed in a liquid etching solution. Numerous problems are encountered when using liquid etching solutions including difficulty in controlling the etching rate, staining of the circuit board and disposing of hazardous liquid wastes.
The most advanced devices manufactured to date have tightly controlled geometric features of less than one micron. These small dimensions preclude the use of liquid etchants. Tremendous interest exists in developing "dry" etching methods in which the etchant is applied and removed in the vapor state. The use of such dry etching methods requires that the etch products have sufficient volatility to effect essentially complete removal from the surface to be etched.
Manufacturers are continually searching for etching agents and processes for using the same which eliminate the above-mentioned problems wherein high quality circuit assemblies can be fabricated without using reagents which are harmful to the environment.